Protective device



PROTECTIVE DEVICE Filed March '7, 1932 /2 /lj .n I ra MJ l f i.

' I gfx/vento@ u w, 5m /MMfwM/K UNITED STATES PATENT OFFICE 2,010,814 PROTECTIVE DEVICE William G.

The Ohio Ellis, Philadelphia, Pa., assis-nor to Electric Manufacturing Company,

Cleveland, Ohio, a corporation of Ohio Application March 7, 1932, Serial No. 597,181 2 Claims. (Cl. 20L-76) This invention relates to a means for protecting electrical machinery from line surges or overgized and de-energized at intervals.

In many such devices at the'instant of breaking the circuit for de-energization the conditions for generation of current are fullled. This gives lise to line surges or over-voltages as is well understood by those skilled in the art.Y

I am aware that prior to my invention it has been recognized in tlie art that some protective device for this type of system is necessary and various means have been provided for that pur- Dose. I have found that the complicated mechaconsiderable quantity of energy in the absence of line surges.

portion of the containing box cut away; Fig. 3 is an enlarged fragmentary detail section; and Fig. 4 is a. schematic showing of the connections involved.

Referring now to the drawing, the numeral I indicates a sheet metal box bottom upon which the protecting elements are mounted and Il denotes a cover therefor. The special material employed as a. resistance unit is formedV into a pair of disks l2 which are clamped between plates i3 and Il. A plurality of bolts l5 pass through the plates I3 and I4, being insulated therefrom Il into clamping relation` to the disks l2. The bolt I5i passes through the bottom l0 and is xedly secured thereto by means of a nut 20. The various bol are of the same construction. The bottom l0' vmay be provided with suitable ears 2l for seeurement of the box to a suitable support. The plates I3 and I4 are preferably 5 provided with radiating ns whereby to dissipate the heat generated by the device during overload conditions.

In Fig. 4 I have shown a double pole switch S inserted in a line which of course receives its supply of current from a suitable alternating or direct current generator. The device shown in the irst three gures of the drawing is indicated schematically by simply showing the plates I3 and I4 with the disks I2 clamped therebel5 tween. The load indicated by the words To load in Fig. 4 will be comprised of or at least include electric machinery such as direct or alter- Dating current motors, transformers or the like.

The disks l2 are composed of special material 20 designed to have a hyperbolic resistance-current characteristic. Such a material is described at length both as to the method of producing it and its characteristics in United States Letters Patent No. 1,822,742 issued to K. B. McEachron on VSsn-member 8, 1931, and is known at thyrite.

with greater or less success. It is suilicient that the material 'should have the property of high resistance at low voltages and much lower resistance at over-voltages such as are apt to be encountered as ance of the protecting device whereby large cur- 'rent will ow through the protecting device and relatively small current will flow through the load. A 56 `mount the same on said base plate, and a cover member telescoping said base platesubstantially as described.

2. A resistor of the character described comprising a pair of metallic plates, one or more disks conned between said pair of plates, the opposite faces of the disk or disks being in contact with said plates, a base member, a plurality of bolts projecting from said base member and extending through said plates and insulated therefrom and spring means resiliently supporting said plates and urging them toward each other and into firm contact with said disk or disks, said disk or disks being formed of a material having a hyperbolic resistance-current characteristic.

WILLIAM G. ELLIS. 15 

